Field of the Disclosure This disclosure relates to a wastegate assembly having an actuator for controlling a wastegate valve adapted for use with turbochargers. More particularly, this disclosure relates to a contoured side wall that is radially offset from a port valve side adjacent to the wastegate port as part of the wastegate assembly.
Description of Related Art
Advantages of turbocharging include increased power output, lower fuel consumption and reduced pollutant emissions. The turbocharging of engines is no longer primarily seen from a high-power performance perspective, but is rather viewed as a means of reducing fuel consumption and environmental pollution on account of lower carbon dioxide (CO2) emissions. Currently, a primary reason for turbocharging is using exhaust gas energy to reduce fuel consumption and emissions. In turbocharged engines, combustion air is pre-compressed before being supplied to the engine. The engine aspirates the same volume of air-fuel mixture as a naturally aspirated engine, but due to the higher pressure, thus higher density, more air and fuel mass is supplied into a combustion chamber in a controlled manner. Consequently, more fuel can be burned, so that the engine's power output increases relative to the speed and swept volume.
In exhaust gas turbocharging, some of the exhaust gas energy, which would normally be wasted, is used to drive a turbine. The turbine includes a turbine wheel that is mounted on a shaft and is rotatably driven by exhaust gas flow. The turbocharger returns some of this normally wasted exhaust gas energy back into the engine, contributing to the engine's efficiency and saving fuel. A compressor, which is driven by the turbine, draws in filtered ambient air, compresses it, and then supplies it to the engine. The compressor includes a compressor wheel that is mounted on the same shaft so that rotation of the turbine wheel causes rotation of the compressor wheel.
Turbochargers typically include a turbine housing connected to the engine's exhaust manifold, a compressor housing connected to the engine's intake manifold, and a center bearing housing coupling the turbine and compressor housings together. The turbine housing defines a volute that surrounds the turbine wheel and that receives exhaust gas from the engine. The turbine wheel in the turbine housing is rotatably driven by a controlled inflow of exhaust gas supplied from the exhaust manifold.
This disclosure focuses on a wastegate assembly disposed in the turbine housing of turbochargers. A wastegate assembly includes a valve, vent and/or bypass that is able to route a significant portion (an example being about 30 percent) of the exhaust gas around (i.e. bypassing) the turbocharger turbine, in order to limit/control turbine work, thus only selectively utilizing a fraction of the available exhaust energy when appropriate. The wastegate assembly by selectively allowing exhaust gas to bypass the turbine wheel reduces the turbocharger's output (or boost). Thereby, the wastegate assembly regulates exhaust gas flow and ensures that the turbine wheel is not spun at an undesirable speed.
Exhaust gas flow is regulated (i.e. some bypassing) though the turbine stage, in order to control turbine work, thus selectively using a fraction of the available exhaust energy. Decreasing the degree of opening of the wastegate valve reduces the amount of exhaust gas that is allowed to bypass the turbocharger turbine, which should increase the amount of pressurized air to the intake manifold. Additionally, or optionally, the engine controller may be configured to decrease the duration of opening of the wastegate valve. An actuator can adjust the amount of exhaust gas that bypasses the turbine through the wastegate assembly.
A turbocharger with a wastegate assembly often has a mechanical actuator for controlling the wastegate valve. The actuator may actively control flow channel geometry with flow control through the wastegate (bypass) port. The actuator of the wastegate assembly may include an arm assembly with a lever arm from a pivot point with a valve head on the lever arm's end that selectively covers a wastegate port. Similarly, the valve head may operate on an arm as a valve rod of a poppet valve or similar non-pivoting valve.
Exhaust gas flow through a wastegate valve actuated via a pivotable lever arm is typically choked, i.e. flow is controlled by the valve curtain area (flow throat area). It is often desirable to use a short lever arm to reduce hinge movement (and packaging constraints). This results in very large and non-linear changes to the curtain area (and resulting flow) with small actuation angles.
Referring to FIG. 1, a conventional turbocharger includes a turbine housing 100 having a wastegate assembly 112 in communication with the volute passage 118 in the turbine housing 100. The turbine housing 100 has a wastegate port 114 that allows exhaust gas flow to bypass the turbine wheel. A wastegate assembly 112 is used to control exhaust gas flow through the wastegate port 114. The wastegate assembly 112 may include a valve 116 that is moveable with respect to the wastegate port 114 for blocking and unblocking the wastegate port 114 thereby controlling the exhaust gas flow, wherein some exhaust gas flow can bypass the turbine wheel to control turbine work in that the turbine wheel rotates at controlled speeds, and thus the maximum boost pressure provided by the compressor. The wastegate port 114 allows bypass gas flow via a valve curtain area Avc. The flow through a wastegate valve 116 in the turbine housing 100 is choked throughout most of its operating range, i.e. the flow rate through the valve 116 is determined by the valve curtain area (flow throat area) Avc. FIG. 5 includes the baseline flow rate for a conventional wastegate valve 116. On a pivoting valve such as wastegate valve 116 that is actuated by a lever arm 120 that pivots about a pivot point 124, an undesirable correlation can result between the actuation angle and the resulting flow rate. For example, the flow rate increases rapidly with actuator angle at small valve opening, but becomes increasingly insensitive to actuator angle the more the valve is opened. This is shown in FIG. 5 by an initially quick increase in mass flow at smaller valve opening angles, then a substantially flat line at the top right of the baseline conventional wastegate valve at a valve opening angle beginning at about 23 degrees, as an example.
Thus, there is a need for more gradual changes in the valve curtain area Avc, and consequently finer control of valve opening and exhaust gas flow.